Various aspects of research in thyroid function and iodine metabolism are under investigation as follows: 1. Purification of thyroid peroxidase and determination of its chemical and physical characteristics; 2. Determination of the role of thyroid peroxidase in iodination and in thyroxine biosynthesis; 3. Elucidation of the mechanism of iodination of thyroglobulin and of the mechanism of iodothyronine biosynthesis; 4. Elucidation of the mechanism of action of the clinically used antithyroid drugs; 5. Studies of the changes in iodine metabolism and in thyroid function that accompany mild and severe iodine deficiency; 6. Assay of thyroid peroxidase in normal and abnormal human thyroid tissue; 7. Measurement of serum T4 and T3 in Rana catesbiana tadpoles at various stages of metamorphosis. BIBLIOGRAPHIC REFERENCES: "The Mechanism of Action of the Thioureylene Antithyroid Drugs" by Alvin Taurog. Endocrinology 98:1031, 1976. "Variations in the Response of the Thyroid Gland of the Rat to Different Low-Iodine Diets: Correlation with Iodine Content of Diet" by G. Riesco, A. Taurog, and P.R. Larsen. Endocrinology 99:270, 1976.